A mathematical model based on conditional probability distributions is proposed for solute yield response to rainfall impulses at the basin scale. Solutes enter the mass balance because of sorption processes between fixed phases and the carrier flow. The present approach addresses the individual role and the mutual connection of the hydrologic response and of macroscopic sorption kinetics controlling basin scale release processes. Mass response functions from geomorphology and statistical mechanics are derived and used to analyze experimental records. A synthesis of nonlinear effects in the mechanism of chemical supply to the carrier and the derivation of concentration distributions are also attempted. -from Author